High-temperature packing



Feb. 2, 1954 J. R. BOYER EIAL 2,667,684

HIGH-TEMPERATURE PACKING Original Filed June 21. 1949 2 Sheets-Sheet lINVENTORS JOHNR. BOYER and, RICHARDM.LUCKRING ATTORNEY.

1954 J. R. BOYER ET AL HIGH-TEMPERATURE PACKING 2 Sheets-Sheet 2Original Filed June 21, 1949 1 1 1 1 l l l l INVENTORS: JOHN R BOYER andBY ICHARD M. LUCKRING ATTORNEY.

Patented Feb. 2, 1954 UNIT 4 PATENT? OFFICE.-

HIGHJ B ATURET PACKING! JohnR; Boyer; Avondale, Pm, andiRi'chardcMi.Luckring; Par-lib,- N. J., assignors tmE: 1. due

Bont de. Nemours; & Company, Del a cprporatiqniof Delaware:

Original application June 2-15, 1949; Serial No; 100,452: Dividedandthis application August 29; 1951-; Ser-ial N. 244,251: A

Thisinvention relates-to azmethodiofrmanuface turingatemperature-resistant fibrous. packing and sealing composition; and moreparticularly; tora method of making such: aa composition that is capableof withstanding high temperatures: in chemical and similar operations.andi atrthe same time will permit relative expansion-1 between joinedtubes: fabricated; from similar or widely difierent 'materials.

Ordinary pacliings or sealing materials :are.-.:ene tirelyunsuitable forhigh temperature. operations; particularly-operationsconductedat 800?to:l0.00" C: and higher; because they: burn: or: fuse; and theircharacteristics changeorthei-r composie tions are partially or entirelyalteredi Also, in many-processes where highly reactive gases must bepumped througlitubesajoints; and the-like, an-efiect ive*sealihg mediumis required to resist; thechemical actionaccompaniedbyhiglgrtemperatures toavoid leaks: and resulting damage.

A further serious problem is the relatively great thermal expansioncompensation: which mustbe provided between tubes ofi the same or,difierentmaterials over the verygreattempera'- ture range involvedin'many-manufacturingop erations- Insome processes, for example; itisecessary to use silicaor other ceramic tubes for certain; portionsoftlg'eprocess apparatus where subjected to exposure to'the' veryl'iighesttemperatures and the relatively low tensile strength of" someofthesematerials renders joinder, a very-dificult problem. Furthermore; silifia or other ceramic tubesfrequently have an eccentric cross sectiondueto inaccuracies in the forming process; and the exact' registering onmating I over. the; entire cross-sectional area of any two tubes tobejoined; isgenerally-impossible:

This inventionhas as anobj ect -asolution 'of the foregoing problems andto provide a methoetof manufacturing athermallyandchemically-resistant,unitary construction which may beretained in position in a number crways to'be described, hereinafter:

A further object, is the productionofi a safe and economical materialfor tigh-tly joining process tubing conveying materials-under veryhightemperatures; particularly-in the region: above BOO C. A- still-furtherobje'ct is the production Off'SllCh a material that will permit:relative expansion and Jthe reIief of 1 thermal stressesibee tweenjoined; members; Another object; is the production of a materialcapablea-of-gtightly join-1 ingprocess tubingzconileying materials velyrhigh temperatures where the tubes areef-abricateda ZQl imS: (01.28

from ;the; same; or: differentimaterials; 1 such; as: all: silica,partly: silica}, and: partly metal; or: entirely metal.

Still; another:- 01315612 is. the: production? ofi a material: for:tightlyssealing on: entirely:" the; ends accomplishedbymakingmas-ilicaiyarn in: tightly wovenor braided forms. the;interstices of: which are 5 pref erablyzsealed with at temperatureresisteant, particulate material;, the packingzbemg re= tained in; placeby; a stuffing box constructiona 102-. cated at the point: of; sealingin'- the; manner hereinafter: described: and illustrated in the; acecompanying drawings in which-: 1

Figure 1: shows one form. of: braided packing constructionhmade inaccordance: with thiszine vention, with; successive braid; layers:stripped backto more; clearly: show: theimethodr of? man catiom.

Figure 23 'shows;a :squared?form ofrpackingring made in: accordance:-withz this: invention:

Figure; 3? ShUWSiOIlBii'GIZlbOdi'HIt-llllit 0t high;tem=.-perature"-joint'.z packed with: rings;- of: the type shown in Fig-ureemFigureAiisa plamviewsof: a lanterniringi The: individual strands: ofthe" packing? mate rial of this inventiongareiformect by twisting-a toegether'small: di'ameteriyarnswftsilica'obtainediby the: extrusion; of?molten: silica: into: ascooling mediums Thee yarn'sz so formed arepreferably substantiallyrpureesilicaibut-tmaymontain'minor amounts .ofrzirconium ..magnes-iumfor aluminum compounds-and may:also;containfspectrographic tracesxof'sodium, calcium; titanium; barium;iron; copper andiboron": salts. Silica yarn-s of? about 0.04'6-inchdiameter; corresponding. to about- 615 denier, have proved satisfactory'for thepurposes of this invention; The-individual yarmfibers arepreferably *loosely itwistedi into: bundles-. of about twe1ve fiberseach; an'd 'ltwo of these-= bundles are then twisted'iinto a sin' glstrand-. A pl'aited braid may: b'e ma'dezup' of' anwnumb'er of 5 thesestrands;'so:long as the 'resulti'ngirope 'is'sufilcientl? fiexibletopermit th'e formatiom of a: coilishape such as*is-zhereinafterdescribed? We havedEound that tabraid ovembrai'd construction iS T'WBIEsuit+ ed to -thespurposesicontemplateds It hasabeenifound thatthe-silica,s randsiormed as;de ribeda o have a: relativ l flow-stre th;

. and a o tend te ray W .3. ra dingrm eliine o leth r ic-one preierahlesto coatthese. strands.with asuitable lubricant'prior to braiding.Furthermore, the strands are somewhat porous in nature, due to the factthat the individual fibers from which they are formed will not withstandthe stresses of hard twisting necessary to produce a relatively densestructure, and it is therefore desirable to seal the void spaces with asuitable sealing agent.

We have found that microcrystalline wax, or

the commercial product known under the trade name of Caloria Oil, areeffective as lubricating materials for our purpose. For the sealant weprefer to utilize graphite, either admixed with the lubricant, orapplied separately to the fibers, as hereinafter described. It will beunderstood however that other sealing materials may be used to meet therequirements, provided they are capable of withstanding the very hightemperatures and the chemical environments to which the packing will besubjected in service. This is not necessary, however, in the case of thelubricating material, since it will have served its purpose when thebraiding operation has been completed.

If the chemical process materials in flow are not reactive with any ofthe individual materials hereinafter listed, amorphous silica, titaniumdioxide, tantalum oxide, or other like manufactured or naturallyoccurring materials, either singularly or in mixture one with another,may be substituted for the graphite. Also, aluminum oxide may beemployed as a sealant, providing the process gases are free fromsubstantial amounts of acids. The particle size of the sealant materialis not particularly critical, sizes ranging from about micron to about50 microns being entirely suitable.

, When microcrystalline wax is used as a lubricant, application may beeffected by merely passing the individual strands through a molten bathof the material disposed between the storage spool and the braiding headof a conventional braiding machine. Satisfactory results are alsoattained when the microcrystalline wax is dissolved in a suitablehydrocarbon solvent, the strands being processed by continuous transittherethrough in the same manner as when molten material is used. SinceCaloria Oil is liquid at room temperatures, it is easily applied bysimple dip bath techniques.

The graphite or other sealant may be applied by simply dusting liberalquantities of the powdered material onto the strands as they emerge fromthe lubricant-applying bath, or, in the alternative, the sealant may bedusted on the outer braided jacket after each successive pass throughthe braiding machine. The amount of sealant take-up is not critical solong as the individual strands give the visual appearance of beingfairly evenly coated. In one analytical determination of the amount oftake-up it was found that 18% of dry graphite was deposited upon asingle strand, made up of 24 individual threads, based on the dry weightof the silica.

The structure of the packing contemplated in this invention ispreferably of the conventional type known in the trade asbraid-over-braid. Referring to Figure 1 the unit packin consists of anydesired number of individual braided serv ings superimposed one onanother until a composite bundle of the desired size is attained. Thisfabrication is accomplished by passing the braid through the braidingmachine a number of times, and increasing the number of individualstrands as the circumference of the braid is built up so that theindividual strands lie quite close together. The resulting rope isfinally passed through a pressing die which compresses the constructionto a generally square or rectangular cross section without, however,loosening the individual strands of the braid or substantiallydecreasing the compactness. The resulting structure is a relativelydense, compact, linearsided rope, the interstices of which are sealed bythe successive braid layers and the sealant compound to present aminimum of channels for the passage of fluids therethrough. If thebraided rope is lubricated with a wax solution, it is preferably driedby heating to a temperature of about C. before further forming.

The dry braided rope may then be cut into the lengths required forindividual packing members. Where the packing is to be used attemperatures up to about 300 C., no allowance need be made forshrinkage. However, at temperatures in the neighborhood of 1000 C. thebraided rope will shrink about 14% in cross sectional area andapproximately 10% in length. Therefore, for application to anyparticular location, material of oversize dimensions within theshrinkage range indicated should be selected. The oversize pieces arepreferably preshrunk before installation by coiling them loosely about aceramic or metal pipe length having approximately the diameter which isrequired forthe inside of the finished packing, theshrinkage-compensating excess at the ends being disposed sideby-siderather than being superimposed. The packing lengths are thereaftersubjected to a pre-shrinking treatment by heating to a temperature ofthe order of 1000 C. in an inert atmosphere, such as nitrogen gas, forexample, to prevent oxidation of the graphite coating.

A typical cycle of heat shrinking may include heating the packing toabout 300 C. over a period of about one hour in a flowing stream ofnitrogen gas and retaining the material at this temperature for abouttwo hours, until all residual oil is driven off. Thereafter, thetemperature may be raised to 900 to 1000 C. in increments of about 100C. per hour in a static nitrogen atmosphere. The material is preferablymaintained at 900 to 1000 C. for about two hours after which heating maybe discontinued and the material cooled by radiation to room temperaturewhile still in the protecting nitrogen atmosphere. During this processthe hydrocarbon lubricant chars away and is lost from the packing, butthis is not disadvantageous since the lubricant will have already servedits full purpose in the braiding operation. After the heat treatment,the individual pieces may be cut on a bias at the ends so that the twobeveled edges will fit together in a neat lap joint when the pieces arearranged in ring form (as in Figure 2).

Referring to Figure 3, silica tube 2 is shown joined in expansiblerelationship to metal tube 3 by virtue of its. telescopic mountingwithin the end of tube 3. The clearance allowance between the memberswill, of course, depend upon the materials of construction of both thetubes, the dimensions of the tubes and the temperature at which theprocess is to be conducted.

The outer end. of metal tube 3 may be expanded into a bell mouth a ofsufiicient diameter to accommodate the individual packing rings 1snugly. The rings are retained in compressed condition by a gland member5 secured to the bell mouth by bolts 6 arranged equidistantly around thecircumference.

g een-sea rferable' to positic'n ng ring indiv-idua'lly, This gland inember register with -those bf adia'cen-t rings to pr'esent a deviousipaith toany leakage which might etherwise scour.

l he .l'j oint of --F'igure '3 is shown fitted with a metal 3 lantern"ring 1 intermediatew located lo'etween the severalspackingmings1|. Theuse of lantern ring I is optional, depending upon the procssmaterialspassingth'rough tubes Zand 3. if thes'e materials are-of andkidizingo'rjfc'hemically corrosive nature they may "degrapliitiae or attack thepacking ring -materialfparticiilarly at the very high temperaturesemployed. The piped materials may be prevented from ever contacting thepacking ring material by flooding the interior of bell mouth 4 with aninert gas, such as nitrogen, for example, which may be supplied throughline 8 leading to a suitable source under pressure. The lantern ringserves as a distributor for the even supply of inert gas throughout theinner confines of bell mouth 4. The use of a lantern ring may also beadvantageous in another connection, namely, that of assisting in theprevention of process material leakage when the joint may not be drawnto maximum tightness in order to provide play to accommodate theconsiderable thermal expansions which accompany very high temperatureoperations.

As shown in Figures 3 and 4, lantern ring I is recessed on oppositesides to provide continuous inner and outer gas channels around theentire circumference of the ring. Drilled holes 9, equally spaced aboutthe ring, connect the inner and outer channels and serve as passages forthe equalizing of gas pressure on both sides of the ring. In operation,the inert gas is supplied through line 8 at about the same or at aslightly higher pressure than that carried in the system comprisingtubes 2 and 3. We have found that leakage of inert gas into the processpiping is negligible if a careful pressure balance is thus maintained.

If the process materials are not of an oxidizing 01' corrosive nature,lantern ring 7 and line 8 may be dispensed with and the space occupiedby ring 1 may be utilized for the accommodation of another packing ring.This is particularly true if gland 5 is relatively close fitting, sincevery slight, almost undetectable, leakage of process material throughthe packing will maintain the bell mouth t free of atmospheric air andthus prevent deterioration from this cause.

The packing made in accordance with this invention also is suitable forclosing off the open end of a single tube. This may be done by providingthe tube with a stuffing chamber that may be either integral with thetube or which may be a separate element adapted to slide over the end ofthe tube. In both cases the levelof the open end of the tube may becarried above" the bottom of the stufiing chamber, thereby providingspace 6 "for the reception df' tlie' pabking material.

method in which it is used. Eon-instance, fithe rlati :row iiiherefitstrength of the is'ilica y b e 'reinfdrcdiih various wayszkncwn to thei1 extiie ai 't,- siich 'as by the (incorporation of a single ce'nt'r'althread of relatively liigh strength i material in -tl i'e fbr'mation ofthe iixfdi a: vial braidin s'tra'h 'a hus, ia'lfine' ectton streamersizc, niay fbe usedfasa ms andth-ef silicaihbers wound-iinto:strandiarmmd it. "true ce-nun thread readily withstands ith'e strainsiifidrit to the braidihg step. When the bcmpesite braih is e'trpbs'ed tbhigh :temp-eratures to effect the pre-shrinking hereinbefore described,the central cotton threads will burn away; however, since the cottonoccupies only a relatively small area within the individual strands,and, since the shrinkage of the silica is relatively high, the burningaway of the cotton does not noticeably aifect the tightness or thedensity of the braid. A like reinforcement may be attained by thesubstitution for the cotton thread of a very fine,temperature-resistant, metal thread, such as nickel, for example,whereupon the metal is not affected by the high temperature shrinkingstep and remains in the packing. braid in unaltered condition.

Such a braided packing ring construction is advantageous because of thehigh density and the avoidance of pores. However, rolls of cloth wovenfrom silica thread and cut on a bias to permit a close fitting withinthe packing space will give reasonably satisfactory results,particularly if treated with graphite or other sealant in the mannerherein described for the braided embodiment. A certain amount of sealingefiect can even be attained by packing joints with a random mass of freesilica fibers. In this case improved sealing can be obtained if thematerial is packed in small individual batts liberally dusted with asealant such as powdered graphite, each batt being compressed afterplacement to secure a relatively dense structure throughout and toassure a minimum of void space. Also, silica packing which has becomedegraphitized by progressive oxidation over a. long period of use willstill be moderately effective; however, leakage will increase as thepercentage of voids increases due to the removal of the graphitesealant.

The joinder of tubes in accordance with this invention may be efiectedin a great number of ways, as by butt to butt positioning, theinterposition of bellows type expansion take-up members between the tubeends, and in many other ways well known in the art. It will be furtherunderstood that, while the product of this invention has been describedwith particular reference and applicability to chemical manufacturingoperations, it is equally applicable for other purposes where a hightemperature, resilient packing material is required, such as in thefield of airplane engine construction and like activities. We intendtherefore to be limited in the scope of out 7. invention only to theextent indicated in the appended patent claims. a This application forpatent is a division of our copending application covering HighTemperature Packing filed June 21, 1949, Ser. No. 100,452.

We claim: v 1. The method of manufacturing a temperanure-resistantfibrous joint packing formed into strands from a number of substantiallypure silica fibers, comprising coating a plurality of the strands with alubricating material and a particulate temperature-resistant sealingmedium, plaiting said strands into a succession of superimposed layersdisposed one over another to form a composite braid, preshrinking theresulting composite braid by exposure to temperatures of 800 to 1000 C.in an atmosphere of an inert gas, and cooling the braid to roomtemperature.- ,'2; The method of manufacturing a temperature-resistantfibrous packing formed into strands from :a number of substantially puresilica fibers, comprising coating a plurality of the strands withaliquid phase hydrocarbon lubricant and powdered graphiteplaiting saidstrands into a succession, of superimposed layers tightly disposed oneover another, pr eshrinking the resulting composite braid by exposure totemperatures of 800 to 1000" C. in an atmosphere of an inert gas for apredetermined time to attain dimensional stability at said temperatures,and then cooling the braid to room temperature.

9 JOHN R. BOYER. RICHARD M. LUCKRING.

References Cited in thefile of this patent 1 UNITED STATES PATENTSNumber Name Date 1,580,199 Hering Apr. 13, 1926 2,107,295 Hawley Feb. 8,1938 2,234,986 Slayter et al Mar. 18, 1941 2,272,588 Simison Feb. 10,1942 2,337,986 Fry Dem-28, 1943 2,393,530 Harris Jan. 20, 1946 2,509,290Elvin et a1 May 30, 1950 FOREIGN PATENTS Number 7 Country Date 30,313Norway Mar. 29, 1917 165,052 Great Britain Dec. 28, 1921 844,748 FranceJuly 31, 1939

1. THE METHOD OF MANUFACTURING A TEMPERATURE-RESISTANT FIBROUS JOINTPACKING FORMED INTO STRANDS FROM A NUMBER OF SUBSTANTIALLY PURE SILICAFIBERS, COMPRISING COATING A PLURALITY OF THE STRANDS WITH A LUBRICATINGMATERIAL AND A PARTICULATE TEMPERATURE-RESISTANT SEALING MEDIUM,PLAITING SAID STRANDS INTO A SUCCESSION OF SUPERIMPOSED LAYERS DISPOSEDONE OVER ANOTHER TO FORM A COMPOSITE BRAID, PRESHRINKING THE RESULTINGCOMPOSITE BRAID BY EXPOSURE TO TEMPERATURES OF 800* TO 1000* C. IN ANATMOSPHERE OF AN INERT GAS, AND COOLING THE BRAID TO ROOM TEMPERATURE.